1. Field of the Invention
The present invention relates to a piezoelectric driving device and its fabricating method, particularly to a piezoelectric driving device used for an actuator or the like for performing precise position control and its fabricating method.
2. Description of the Prior Art
In recent years, the recording density of a magnetic disk set at a magnetic disk drive has been continuously improved at an annual rate of 10%. A magnetic head used to record and reproduce data in and from a magnetic disk is normally mounted on a slider and the slider with the magnetic head mounted on it is supported by a head-supporting mechanism set in a magnetic disk drive.
To improve the recording density of a magnetic disk, it is necessary to very accurately position a magnetic head with respect to the magnetic disk. To realize the above mentioned requirement, a piezoelectric driving device using a piezoelectric-member element is set at a head-supporting mechanism. In the case of the piezoelectric-member element of the piezoelectric driving device, an electrode metallic film is formed on both principal planes of a thin-film piezoelectric member. When a voltage is applied between the two electrode metallic films, the thin-film piezoelectric member expands or contracts in the in-plane direction. Position control of a magnetic head is accurately performed by using the fluctuation due to the above telescopic motion (e.g. refer to Japanese Non-examined Publication No. 2001-216748).
In the case of the above thin-film piezoelectric-member element, a voltage is applied to an electrode metallic film through a bonding wire joined to the surface of the metallic film. The bonding wire is joined to a predetermined position on the electrode metallic film through ultrasonic joining.
However, during ultrasonic-joining of a bonding wire to an electrode metallic film, damage such as a crack occurs in an electrode metallic film and thin-film piezoelectric member, and moisture and steam enter the electrode metallic film and thin-film piezoelectric member. Thereby, the metal in the electrode metallic film ionizes, diffuses in a thin-film piezoelectric member between adjacent conductors (electrode metallic films) having a potential difference, and precipitates as a metal on the surface of the opposite conductor again. Thus, because the tree-like conductors are cross-linked by the metal, a problem occurs in that a short-circuit-mode failure (ion migration) occurs. As a result, the reliability of a piezoelectric element deteriorates. The above phenomenon is particularly remarkable under a high-humidity environment.
The present invention is made to solve the above problem, and its object is to provide a piezoelectric driving device in which a short circuit does not easily occur between electrode metallic films even if performing bonding-wire joining and its fabricating method.
To achieve the above object, a piezoelectric driving device of the present invention is a piezoelectric driving device in which a piezoelectric thin plate is joined to one side of a substrate and a terminal electrode for applying a signal for expanding or contracting the piezoelectric thin plate is further formed on the plane. The terminal electrode is formed on one side of the substrate through a piezoelectric-member pedestal separated from the piezoelectric thin plate.
In the case of the piezoelectric driving device of the present invention constituted as described above, because the piezoelectric thin plate serving as a piezoelectric displacement region is separated from the piezoelectric pedestal on which the terminal electrode is formed, it is possible to decrease a mechanical impact or vibrations under wire bonding to the piezoelectric displacement region and prevent a crack or the like from occurring in the piezoelectric thin plate.
Moreover, in the case of a piezoelectric driving device of the present invention, it is preferable that the above piezoelectric thin plate and piezoelectric-member pedestal have the same laminated structure when a plurality of layers are laminated respectively.
Furthermore, in the case of a piezoelectric driving device of the present invention, it is possible to use a substrate which can be expanded or contracted corresponding to expansion or contraction of the above piezoelectric thin plate as the above substrate, or to use a non-retractable substrate which can be deflected as the above piezoelectric thin plate.
In the case of a piezoelectric driving device of the present invention, it is possible to constitute the above non-retractable substrate by fixing a metal thin plate (e.g. stainless-steel thin plate) opposite to the above piezoelectric thin plate and connecting a wiring metal to the above terminal electrode by a resin.
In the case of a piezoelectric driving device of the present invention, it is possible that two piezoelectric-member-driving portions are included and the above piezoelectric thin plate is divided into two plates corresponding to each piezoelectric-member-driving portion.
In the case of a piezoelectric driving device including two piezoelectric-member-driving portions, it is possible to constitute the above terminal electrode by a signal terminal electrode connected to one of the two piezoelectric-driving portions, a signal terminal electrode connected to the other of them, and a ground terminal electrode common to the two piezoelectric-driving portions.
In the case of a piezoelectric driving device of the present invention, it is preferable that the above piezoelectric thin plate has a laminated structure in which a first thin-film piezoelectric-member layer and a second thin-film piezoelectric-member layer on each of whose faces an electrode film is respectively formed are joined by an adhesive, and electrode films facing each other through the adhesive are used as ground electrode films.
In the case of a piezoelectric driving device of the present invention, it is possible to use the above terminal electrode as a wire-bonding terminal.
Moreover, a piezoelectric-member-driving-device-fabricating method of the present invention comprises forming a first electrode, a first piezoelectric-member thin film, and a second electrode on a first substrate and forming a third electrode, a second piezoelectric-member thin film, and a fourth electrode on a second substrate. The above second electrode is arranged to face the above fourth electrode, and they are bonded by an adhesive, thereby pasting the above first substrate with the above second substrate. A piezoelectric-laminated body layer in which the above first electrode, first piezoelectric-member thin film, second electrode, fourth electrode, second piezoelectric-member thin film, and third electrode are laminated between the above first and second substrates is formed. The above second substrate is removed. A part of the above piezoelectric laminated-body layer on the above first substrate is separated to form at least two piezoelectric-member pedestals formed by the separated portion. A first bonding electrode connected to the above second and fourth electrodes is formed on one of the two piezoelectric-member pedestals, and a second bonding electrode connected to the above first and third electrodes is formed on the other of the two pedestals. A transferring substrate is joined onto the above piezoelectric-laminated-body layer and two piezoelectric-member pedestals, and then the above first substrate and transferring substrate are removed. A non-retractable substrate which can be deflected instead of the removed first substrate is joined.
According to a fabrication method of the piezoelectric driving device of the present invention constituted as described above, it is possible to fabricate a piezoelectric driving device in which a piezoelectric-member-laminated body layer functioning as a piezoelectric displacement region is separated from the above piezoelectric-member pedestal on which the above terminal electrode is formed.